Using Axis Commands with Analog Values

[LennyG]

I am looking at controlling a conveyor belt with a VFD and closing the loop with a laser distance gauge. Is there a way to have the Axis trapezoidal or Scurve move give an analog value instead of Pulse output so I can send it to my VFD? Since this is a linear motion, would it be possible to close the position loop with an analog input instead of using pulses from an encoder or a glass scale?

[rlp122]

There is probably a better way to do this, but we would need to know more about your setup.  Not to say it can't be done with an AXIS command, but it probably won't be as easy as another method.

For example, if you are using an encoder, maybe take a look at Rate scaling in addition to position scaling.  You can send the same input signal to more than one HSIO function.  Use the position to check where the target is and the rate to verify how fast it is arriving.  A little math to slow things down as needed.  Maybe use interrupts at certain positions to be sure you are hitting the target.  If you need slopes, there is a function in the analog section for that.

[JasonO]

Yes to the first question. Set up a Virtual Axis to execute your AXIS commands, then take that axis CurrentVelocity value and scale it to give you a value for your analog output. I have done this with a hydraulic system that is controlled by a proportional valve, with an encoder to close the loop, and it worked excellently.

To your second question, it is not possible to directly close the loop with an analog input, when using the high speed axis setup. I believe it should be possible to use an open loop axis configuration, and then add some math based on your analog position input, to trim the analog output to the VFD based on the analog position feedback. I've never done it though, and as mentioned it may be simpler to solve this application some way other than using AXIS commands.